Mono-modification at the C6-Position

6-Tosyl j8-CyDs are important precursors for a variety of modified CyDs because a nucleophile can attack the electrophilic carbon at the 6-position to produce a corresponding functionality. The reaction of jS-CyD with tosyl chloride in aqueous alkaline medium gives mono-6-tosylated jS-CyD in fairly good yield [15]. 

Modifications of C6 of CyD other than by tosylation are very rare. However, a single-step quantitative-yield synthesis of CyD monoaldehydes has been published. The CyD was dissolved in an organic solvent, Dess-Martin perodinane was added, and the mixture was stirred for 1 h at room temperature. Addition of acetone and cooling allowed isolation of the crude product by filtration [16]. Another synthesis was performed by using IBX (l-hydroxy-l,2-benziodoxol-3(lH)-one 1-oxide) as oxidant in DMSO. Mono-oxidation of jS-CyD was performed along with its incorporation into chitosan by a reductive coupling reaction [17]. A direct azidation of CyDs with sodium azide in the presence of triphenylphosphine-carbon tetrabromide has also been reported [18]. 

Starting from 6-monotosyl CyD, many derivatives can be obtained, including aldehyde [19], iodide, chloride, azide, amino-, and alkyldiamino-CyDs. Dimeric yS-CyD receptors were synthesized from mono-6-iodo-CyD with a dithiol core, and they have potential as selective receptors of a-helical peptides [20]. Fullerene derivatives bearing a-, and y-CyD units were synthesized by the reaction of C o and peracetylated CyD 6-azides [21]. From 6-monoazide-yS-peracetylated CyD or 

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